1. Field of the Invention
Metal inserts are frequently embedded in any of various plastic materials, to afford means for receiving mating fastener elements. To this end, a cylindrical insert is conventionally provided, having a threaded bore, such that when the insert is embedded in a recess formed in the surface of a plastic work piece, it will in this way provide a hole or recess having metallic, internal threads, adapted to receive complementary threads formed upon a mating fastener element.
The invention thus may appropriately be said to fall within the field of fasteners generally, and more specifically in that area of this general field relating to the provision of metallic fasteners fixedly embedded in the surfaces of plastic work pieces.
2. Description of the Prior Art
Metallic inserts of the type described above are well known in and of themselves, and in many instances have external threads for the specific purpose of allowing the insert to thread itself into the initially smooth-walled recess of a plastic work piece. Thus, self-tapping inserts are not new in and of themselves. Nor is it new to provide, in an insert of this type, uniformly, angularly spaced flutes. Further, it is also known to taper the ends of an insert of this type.
The prior art, however, has not up until now provided a fully satisfactory solution to the problems encountered in the provision and mounting of threaded inserts of this general type. In the prior art, for example, the flutes are designed to receive chips resulting from the cutting action of the insert threads as the insert taps the hole of the plastic work piece.
Although the prior art inserts, through the formation of the flutes at angularly spaced locations on their circumferences, have to some degree provided an accommodation for the chips from the work piece, it has been found that the chip-receiving function of said inserts has been heretofore discharged with comparative inefficiency. The reason is that there has been no specially, scientifically planned relationship between the flute depths, the cross-sectional shapes of the flutes, the tapered ends of the insert, and the relationship of the flute bottom surfaces to the roots of the threads, that are intended to and do successfully cause the chips to produce a true self-locking action when the insert is fully engaged in the work piece.